Whoever wants a lushly flowering summer bed already in June does not sow outdoors in May, but starts the summer flowers indoors from March. Marigold, zinnia, cosmos and snapdragon germinate reliably on the warm windowsill and are sturdy young plants by the Ice Saints, ready to start straight away.
Starting indoors is simple, but has two stumbling blocks: grown too warm and dark, the seedlings turn long and pale, and planted out too early they are caught by frost. This article shows you how to avoid both.
Why start indoors
Summer flowers sown straight into the bed only start when the soil is warm enough, usually mid-May. Started plants then already have a six to eight week head start and bloom correspondingly earlier and longer. You also get sturdy, even plants instead of patchy direct sowing that slugs love to eat.
Starting indoors is especially worthwhile for heat-loving species like zinnia and for anything you want to set in clear groups in the bed. Robust self-seeders like pot marigold or cornflower you can also sow directly.
From sowing to the bed
Sow from March
Fill trays with poor seed compost, sow the seeds thinly and cover them depending on the species. Light germinators like marigold only press down, do not cover with soil.
Keep bright and warm
Put the sowing in a bright, warm spot around twenty degrees. What matters is plenty of light, otherwise the seedlings turn long and pale. A south window or a plant lamp helps.
Prick out after the true leaves
As soon as the first true leaves show after the seed leaves, you separate the seedlings into their own pots. That gives each plant room and makes it compact.
Harden off for a week
Before the plants may go into the bed, you put them outside during the day for a week in a sheltered spot. That way they slowly get used to sun and wind.
Plant out after the Ice Saints
Only after mid-May, when no more night frosts threaten, do the summer flowers go into the bed. Earlier you risk a late frost ruining everything.
Sow from March bright and not too warm, prick out after the first true leaves, and out only after the Ice Saints. That way your summer flowers bloom early and strong.
The core rule for starting indoors
Frequently asked questions
When do you start summer flowers indoors?
From March, about weeks 10 to 16, on the bright windowsill. That way the plants are sturdy enough to plant out by mid-May and bloom clearly earlier than summer flowers sown straight into the bed.
Which summer flowers can be started indoors?
Almost all heat-loving species: marigold, zinnia, cosmos, snapdragon, morning glory and sunflower. Robust self-seeders like pot marigold, cornflower and poppy you can also sow straight into the bed.
Why do my seedlings grow long and thin?
Because they get too little light and too much warmth. In low light the seedlings stretch toward the window and turn pale and unstable. Put them brighter and a little cooler, then they grow compact.
When may I set the started plants into the bed?
Only after the Ice Saints in mid-May, when no more night frosts threaten. Harden the plants off for a week beforehand by putting them outside during the day, otherwise they get sunburn.
Do you have to prick out summer flowers?
Yes, as soon as the first true leaves show after the seed leaves. Pricking out separates the crowded seedlings into their own pots. That gives each plant enough room and makes it sturdy instead of leggy.
